The present study investigates the effect of language-specific knowledge on iconicity ratings of native and foreign signs. German signers judged the iconicity and similarity of DGS (German Sign Language) and ASL (American Sign Language) signs. We found that iconicity ratings were higher for DGS than for ASL signs, and that DGS signers perceived the ASL signs to be less iconic than ASL signers. Further, iconicity judgements of foreign signs were mediated by the phonological and conceptual similarity of those signs to DGS signs. Overall our results indicate that iconicity is not an ontological attribute of the sign itself, no ‘objective iconicity’ exists. We conclude that the perception of iconic reference depends on an interpreter and is shaped by language-specific experiences.